I would be interested where you came up with that. Can you hook me up?
Sure. Find a blood-alcohol calculator. Guess the guy's weight (based on age, I guessed about 150). Set the "time drinking" to three hours, and keep adding liquor until a 0.12 is reached. Then set "time drinking" to zero and read the result.
Different calculators give somewhat different results, and I didn't know the guy's weight, but the 0.17-0.21 seemed a reasonable range.
Too many variables are unknown to accurately determine how much burnoff this kid had.
You pose a bypothetical and I will return one to you and see what you think about it.
Lets say he had left wherever he was at 15 minutes before he crashed into us. Lets say that right before he left he did four shots with his buddies or did a five foot beerbong.
In this event it is possible that his BAC at the time of the crash was equal to or less than when he blew.
I offer this only to take notice that there is no way to accurately measure such a thing as you attempt to measure without more information.